Circadian Rhythm of the Liver of Male Rats Dosed with Phenobarbital—I. Organ Weight, Cellular Structures, Glycogen Contents and Mitotic Activity

The circadian rhythm of the liver, namely organ weight, cellular structures (by light-microscopy), glycogen content (by periodic acid-Schiff (PAS) reaction) and mitotic activity, was studied in 166 male Sprague-Dawley rats orally treated daily at 0800-0900 with 70 (study 1) or 50 (study 2) mg/kg phenobarbital (PB) for 7days. Thereafter, eight (study 1) or five (study 2) rats each were studied at 4-hr intervals at 1000, 1400, 1800, 2200, 0200, 0600 and 1000 through till the following day. The lighting schedule in the colony was 12:12, light:dark (light from 0600 to 1800). The liver weight was raised in PB-treated rats at all times of the day compared to controls and showed a distinct circadian rhythm with a peak at 1000 and a minimum at 2200 in PB-treated rats and the controls. The circadian rhythm of cellular structures was closely related to the hepatic glycogen content which was in good agreement with the controls, but at 1400 and 1800 the glycogen particles were more distinctly diminished in the enlarged centrilobular hepatocytes of PB-treated rats. The mitotic activity of hepatocytes was markedly increased in rats treated with PB but showed the same circadian rhythm as controls with a peak at 1000.     

Circadian Rhythm of the Liver of Male Rats Dosed with Phenobarbital—I. Organ Weight,Cellular Structures,Glycogen Contents and Mitotic Activity

The circadian rhythm of the liver, namely organ weight, cellular structures (by light-microscopy), glycogen content (by periodic acid-Schiff (PAS) reaction) and mitotic activity, was studied in 166 male Sprague-Dawley rats orally treated daily at 0800-0900 with 70 (study 1) or 50 (study 2) mg/kg phenobarbital (PB) for 7days. Thereafter, eight (study 1) or five (study 2) rats each were studied at 4-hr intervals at 1000, 1400, 1800, 2200, 0200, 0600 and 1000 through till the following day. The lighting schedule in the colony was 12:12, light:dark (light from 0600 to 1800). The liver weight was raised in PB-treated rats at all times of the day compared to controls and showed a distinct circadian rhythm with a peak at 1000 and a minimum at 2200 in PB-treated rats and the controls. The circadian rhythm of cellular structures was closely related to the hepatic glycogen content which was in good agreement with the controls, but at 1400 and 1800 the glycogen particles were more distinctly diminished in the enlarged centrilobular hepatocytes of PB-treated rats. The mitotic activity of hepatocytes was markedly increased in rats treated with PB but showed the same circadian rhythm as controls with a peak at 1000.     

Plasma hyaluronan concentration: no circadian rhythm but large effect of food intake in humans

This study was designed to determine if a circadian rhythm in plasma hyaluronan concentration [HA] exists in the absence of physical activity, and if plasma [HA] is associated with feeding in human subjects. Five persons were studied under standardized conditions, blood samples being taken between 0600 and 2200 hours at 30-min intervals. Any orthostatic challenge and muscle activity was abolished by immobilization by a 6° head-down bed-rest, and the effect of a quasi-continuous ingestion of energy compared a normal, three-portion diet of equivalent energy content or to fasting. Reproducibility of HA profiles on two consecutive half-days was also studied. A highly sensitive immunoassay was used to determine plasma [HA]. The data indicated that without physical activity and without food ingestion, [HA] was unchanged and displayed no diurnal rhythm. In addition, we observed that [HA] increased after the first food intake, peaking after 60 min, and concluded from our results that without ingestion of a larger meal, and sessions of postural or muscle activity, no circadian plasma [HA] rhythm exists. Accepted: 10 June 1998     

Serum corticosteroids at the high and low points of the circadian rhythm in rats with regenerating adrenals.

Serum levels of 11-deoxycorticosterone (DOC), 18-hydroxy-11-deoxycorticosterone (18-OH-DOC) and corticosterone (B) were determined at the high (1800 h) and low (0800 h) points of the circadian rhythm in control rats and in rats with regenerating adrenals. The levels of DOC at 0800 h in quiescent rats with regenerating adrenals were 6.5 times greater than in the control group. The levels of 18-OH-DOC and B, however, were not significantly different between these groups. A circadian rhythm for B, 18-OH-DOC and DOC was evident in control rats with a 12,20 and 3.5 fold increase, respectively, at 1800 h as compared to 0800 h. In animals with regenerating adrenals there was only a minimal change in the levels of B and 18-OH-DOC at 1800 h. There was, however, a 2 fold further increase in the levels of DOC at 1800 h as compared with the elevated levels at 0800 h. These findings show that the decrease in 11β and 18-hydroxylase activity of the regenerating adrenal is most clearly evident at the high point of the circadian rhythm. Furthermore, only by taking into account physiological variations in adrenal activity can an accurate assessment of DOC secretion in the adrenal regeneration model of hypertension be obtained.     

Histochemical demonstration of a circadian rhythm of succinate dehydrogenase in rat pineal gland. Influence of coenzyme Q10 addition.

Succinate dehydrogenase activity was investigated histochemically in the rat pineal gland. The influence of fixation on the activity pattern, the possible diffusion of enzyme, the nothing dehydrogenase reaction, and the substantivity of the tetrazolium salts and formazans were investigated in control experiments. In rats maintained on a 17/7 h light/dark schedule a distinct circadian rhythm of the succinate dehydrogenase was demonstrated in the pineal gland. Activity was lowest during the day and highest during the night. The dorsocaudal part of the gland showed the highest activity and within the same part of the gland the activity varied between individual pinealocytes. A relative lack of endogenous coenzyme Q, as well as a circadian rhythm of this coenzyme, highly influenced the activity of succinate dehydrogenase. It is concluded that succinate dehydrogenase activity in the pineal gland of the rat is regulated by changing the concentration of the active enzyme itself as well as the level of the endogenous coenzyme Q. Whether this is caused by a circadian rhythm in the synthesis or in the catabolism of the enzyme and the coenzyme was not revealed by the present study .     

Circadian Rhythms of Melatonin and Sex Steroids in a Nocturnal Bird, Indian Spotted Owlet Athene brama During Reproductively Active and Inactive Phases

The epiphyseal neurohormone melatonin (MEL) exhibits circadian cyclicity, as noted extensively in diurnal vertebrates although very little information is available regarding nocturnal species. We have studied the MEL rhythmicity with 24-hour periodicity in a tropical nocturnal bird, Indian spotted owlet Athene brama, which possesses a well-developed pineal organ. We performed our study during two crucial reproductive phases (active and inactive), when the pineal gland activity in owlet exists in inverse states, i.e., inactive and active respectively. Independent of sex, the circadian rhythm of plasma MEL in owlets showed a two-peak cyclicity with a smaller peak at around 1400 h and the higher one at about 0200 h, while the lowest value was found at 1000 h. The night (0200 h) peak activity of plasma MEL in owlet has a resemblance with the earlier findings in diurnal birds and strongly suggests that independent of species habit the peak activity of MEL is invariably dark dependent. However, the daytime peak of MEL may be due to the daytime hiding nature of this nocturnal bird. Interestingly, it was also noted that the hours of peak activity of MEL (1400 and 0200 h) were the same during both of the reproductive phases, though the environmental day length was longer and ambient temperature was higher during the reproductively inactive phase. During daytime these birds hide in a dark burrow where, in general, the intensities of light and temperature are less, and the amplitude of variations of these factors is not prominent. Hence, the seasonal variations in these oscillatory components may not have affected the entrainment of the owlet pineal oscillator, which regulates the daily MEL rhythm in a similar pattern during both the studied phases. On the other hand, a single circadian peak (around 1000 h) circadian cyclicity of gonadal steroids (i.e., testosterone in the male and estradiol and progesterone in the female) showed an inverse relationship with plasma MEL. Possibly, MEL regulates the daily steroidogenic status in owlets by an inhibitory influence.     

Phosphoenolpyruvate carboxykinase in mouse pancreatic islets. ATP-induced changes in sensitivity to Mn2+ activation

The presence of high phosphoenolpyruvate carboxykinase (EC 4.1.1.32) activity in mouse islet cytosol has been demonstrated. The enzyme was activated by Mn2+ with a Ka of 100 X 10(-6) mol/l. The mean total activity of the Mn2+-stimulated phosphoenolpyruvate carboxykinase in islet cytosol estimated at 22 degrees C with saturating concentrations of the substrates oxaloacetate and ITP was 146 pmol/min per micrograms DNA. Km was calculated to be 6 X 10(-6) mol/l for oxaloacetate and 140 X 10(-6) mol/l for ITP. The islet phosphoenolpyruvate carboxykinase activity was not increased after starvation of the animals for 48 h. Preincubation of the cytosol at 4 degrees C with Fe2+, quinolinate, ATP, Pi, glucose 6-phosphate, fructose 1,6-bisphosphate, NAD+, NADH, oxaloacetate, ITP, cyclic AMP and Ca2+ had no effect on the enzyme activity. However, preincubation of the cytosol at 37 degrees C with ATP-Mg inhibited the Mn2+-stimulated phosphoenolpyruvate carboxykinase activity progressively with time and in a concentration-dependent manner. A similar but weaker inhibitory effect was observed with p[NH]ppA, whereas p[CH2]ppA, ADP, AMP, adenosine and Pi had no effect. It is tentatively suggested that ATP and p[NH]ppA either by adenylation or otherwise affect the interaction between islet phosphoenolpyruvate carboxykinase and the recently discovered Mr = 29000 protein modulator of the enzyme in such a way - perhaps by causing a dissociation between them - that phosphoenolpyruvate carboxykinase loses its sensitivity to Mn2+ activation.     

Circadian Rhythms of Melatonin and Sex Steroids in a Nocturnal Bird,Indian Spotted Owlet Athene brama During Reproductively Active and Inactive Phases

The epiphyseal neurohormone melatonin (MEL) exhibits circadian cyclicity, as noted extensively in diurnal vertebrates although very little information is available regarding nocturnal species. We have studied the MEL rhythmicity with 24-hour periodicity in a tropical nocturnal bird, Indian spotted owlet Athene brama, which possesses a well-developed pineal organ. We performed our study during two crucial reproductive phases (active and inactive), when the pineal gland activity in owlet exists in inverse states, i.e., inactive and active respectively. Independent of sex, the circadian rhythm of plasma MEL in owlets showed a two-peak cyclicity with a smaller peak at around 1400 h and the higher one at about 0200 h, while the lowest value was found at 1000 h. The night (0200 h) peak activity of plasma MEL in owlet has a resemblance with the earlier findings in diurnal birds and strongly suggests that independent of species habit the peak activity of MEL is invariably dark dependent. However, the daytime peak of MEL may be due to the daytime hiding nature of this nocturnal bird. Interestingly, it was also noted that the hours of peak activity of MEL (1400 and 0200 h) were the same during both of the reproductive phases, though the environmental day length was longer and ambient temperature was higher during the reproductively inactive phase. During daytime these birds hide in a dark burrow where, in general, the intensities of light and temperature are less, and the amplitude of variations of these factors is not prominent. Hence, the seasonal variations in these oscillatory components may not have affected the entrainment of the owlet pineal oscillator, which regulates the daily MEL rhythm in a similar pattern during both the studied phases. On the other hand, a single circadian peak (around 1000 h) circadian cyclicity of gonadal steroids (i.e., testosterone in the male and estradiol and progesterone in the female) showed an inverse relationship with plasma MEL. Possibly, MEL regulates the daily steroidogenic status in owlets by an inhibitory influence.     

Histochemical demonstration of a circadian rhythm of succinate dehydrogenase in rat pineal gland. Influence of coenzyme Q10 addition

Summary Succinate dehydrogenase activity was investigated histochemically in the rat pineal gland. The influence of fixation on the activity pattern, the possible diffusion of enzyme, the nothing dehydrogenase reaction, and the substantivity of the tetrazolium salts and formazans were investigated in control experiments.In rats maintained on a 17/7 h light/dark schedule a distinct circadian rhythm of the succinate dehydrogenase was demonstrated in the pineal gland. Activity was lowest during the day and highest during the night. The dorsocaudal part of the gland showed the highest activity and within the same part of the gland the activity varied between individual pinealocytes. A relative lack of endogenous coenzyme Q, as well as a circadian rhythm of this coenzyme, highly influenced the activity of succinate dehydrogenase. It is concluded that succinate dehydrogenase activity in the pineal gland of the rat is regulated by changing the concentration of the active enzyme itself as well as the level of the endogenous coenzyme Q. Whether this is caused by a circadian rhythm in the synthesis or in the catabolism of the enzyme and the coenzyme was not revealed by the present study.     

Circadian rhythms in digestive enzymes in the small intestine of rats. I. Patterns of the rhythms in various regions of the small intestine.

The activities of the digestive enzymes, maltase [EC 3.2.1.20], sucrase [EC 3.2.1.26], trehalase [EC 3.2.1.28], Leucine aminopeptidase [EC 3.4.11.1], and alkaline phosphatase [EC 3.1.3.1] were measured in various regions of the small intestine of rats. The activities of all these enzymes were much higher in the jejunum than in the ileum, and in the distal regions of the ileum no sucrase, trehalase or alkaline phosphatase activity was detected. In the jejunum, the activities of all the enzymes tested exhibited clear circadian variations with the highest activity at 0000-0400 h and the lowest at 1200 h when the rats were fed ad libitum. In the ileum, maltase and sucrase also exhibited circadian variations, but the amplitude of the rhythm was smaller than that in the jejenum. Trehalase and alkaline phosphatase did not show any circadian variation in the ileum. Leucine aminopeptidase showed a circadian variation in the ileum with the same amplitude as in the jejunum. The phase of the circadian variations shifted about half a day when the rats were fed in the daytime, but the amplitude of the rhythm did not change.     

The circadian rhythm of intra-acinar profiles of alcohol dehydrogenase activity in rat liver: a microquantitative study

Summary Using microquantitative measurements of alcohol dehydrogenase activity in microdissected samples of liver tissue along the sinusoidal length, the intra-acinar distribution profiles were studied in seven groups of female rats at different times during 24h with a light phase from 630h to 1830h. The mean values of alcohol dehydrogenase activity showed a circadian rhythm with a minimum at 13.30h and a maximum at 17.30h (p<0.0001). However, the intra-acinar gradients remained almost unchanged, indicating that increase and decrease in enzyme activity takes place simultaneously in all parts of the liver acinus. This observation, together with data from the literature, suggests that the circadian rhythm of alcohol dehydrogenase activity reflects variations in different liver cell consituents, rather than enzyme protein synthesis or proteolysis.     

Meal feeding schedule and ventromedial hypothalamic lesions do not affect rhythm of pineal serotonin N-acetyltransferase activity in rats

Effects of meal feeding schedule and bilateral lesions of the ventromedial hypothalamus (VMH) on the circadian rhythm of pineal serotonin N-acetyltransferase (SNAT) activity were examined in rats, under LD (12:12) condition. Neither meal feeding nor VMH lesions affected the phase of the circadian rhythm of pineal SNAT activity, but the VMH lesions reduced the level. Meal feeding caused a shift of the phases of the daily rhythms of phosphoenolpyruvate carboxykinase and tyrosine aminotransferase activities in the liver. These findings suggest that the circadian rhythm of pineal SNAT activity is not entrained by the food intake, and that the VMH does not function as a master oscillator of the rhythm.     

模拟空间节律（L：D=0.75h：0.75h）对树qu...

It is known that contemporary space station revolves at the altitude of 400-500 km in the outer space. The present study was undertaken to investigate the effects of simulated space rhythm (L:D = 0.75 h:0.75 h) at this altitude on circadian rhythm in tree shrews (Tupaia belangeri chinensis) and the effects of endogenous sleep inducing neuropeptide Asp5-alpha-DSIP on the space-rhythm-entrained circadian rhythm. This primitive stock serves as one species of Tupaiidae and is a unique native of South China. Our previous studies have shown that this species showed striking differences in natural circadian rhythm between day and night (e.g. 3.03 degrees C of rectal temperature). Results showed that the above mentioned space rhythm (L:D = 0.75h:0.75h) could drastically disturb the inherent circadian rhythm of Tupaia belangeri chinensis. The maximal peak of motor activity dropped significantly in the morning (0600-1200) and a new enhanced peak (more than 20 times greater than that of the control) was found between 1800-2400, whereas the maximal trough of motor activity (2400-0600) remained basically unchanged. Concurrently, the total amount of 24-h motor activity was significantly decreased and the recovery after the cessation of space rhythm was slow. Experimental results also demonstrated that consecutive administration of Asp5-alpha-DSIP (30 micrograms/kg, i.p.) for 5 days (2 days before and 3 days during space rhythm) did not prevent the basic disturbance of circadian rhythm of Tupaia belangeri chinensis caused by the space rhythm (L:D = 0.75h:0.75h). Nevertheless, no decrease or even some enhancement of the total amount of 24th motor activity was observed during space rhythm or after its cessation.     

Reproductive phase depedent circadian variation in the pineal biochemical constituents of Indian palm squirrel, Funambulus pennanti

In mammals, pineal gland is intimately concerned with the co-ordination of rhythm physiology. Biochemical characteristics of pineal gland in man and other mammals may provide strong, yet sometimes elusive support for the belief in functional individuality and probable importance of this tiny gland. In seasonal breeding animals, pineal gland function is very much dependent on the reproductive status. Therefore, the aim of this experiment is to note the circadian rhythmicity of different biochemical constituents of pineal gland during active and inactive phases of reproductive cycle of a seasonally breeding rodent, F. pennanti. In the present study, pineal biochemical constituents i.e. protein and cholesterol showed higher values during daytime (1400 h). The plasma melatonin level presented two peaks during active (April; at 1800 h and 0200 h) and inactive (December; at 1400 h and 0200 h) phases of reproductive cycle. The pineal protein, cholesterol and plasma melatonin values in term of basal and peak levels were higher during the reproductive inactive/pineal active phase. Therefore, pineal--also known to have antigonadotropic properties and cholesterol which appears conjugated with pineal serotonin, presented circadian rhythmicity along with the plasma level of melatonin. This rhythmicity noted in present study was dependent on the reproductive and pineal activity status, and might be regulated by the sex steroid receptor present on the pineal gland.     

Circadian Rhythm of Liver Parameters (Cellular Structures,Mitotic Activity,Glycogen and Lipids in Liver and Serum) During Three Consecutive Cycles in Phenobarbital-Treated Rats

The circadian rhythm of gastric content, serum alkaline phosphatase (alk.P.), serum lipids, body weight (wt), relative (rel.) liver wt, cellular structures (by light- and electron-microscopy), mitotic activity of hepatocytes, glycogen content, protein and lipids in liver was studied in 180 male Sprague-Dawley rats orally treated at 0830-1030 with 50 mg/kg phenobarbital (PB) for 7 days. Thereafter, five PB-treated males and five controls each were studied at 4-hr intervals at 0600, 1000, 1400, 1800, 2200 and 0200 on 3 consecutive days. The lighting schedule in the colony was 12:12 = light/dark (light from 0600 to 1800). Following the rhythm of gastric emptying, the rel. liver wt showed a clear circadian rhythm with a peak at 0800. The rel. liver wt was raised in PB-treated rats at all times of the day. The circadian rhythm of cellular structures was closely related to the hepatic glycogen content which exhibited a clear rhythm with the peak also at 0800, but lowered values were found in PB-treated rats. The mitotic activity of hepatocytes was significantly increased in PB-treated rats but displayed the same circadian rhythm as controls with peaks at noon and troughs at midnight. The well-known hypertrophy of the smooth endoplasmic reticulum in PB-treated rats was not found at 0600, but was fully developed at 1400 and 2200. PB-treatment increased significantly the liver content of cholesterol, triglycerides and phospholipids. Liver cholesterol showed a clear circadian rhythm with peaks at 1800. No rhythm of liver protein, triglycerides and phospholipids was observed. In serum, levels of cholesterol were significantly elevated, those of triglycerides and alk.P. significantly lowered, while those of phospholipids were not affected by the treatment. The three serum lipids, alk.P. and beta-lipoprotein exhibited a clear circadian rhythm, while serum glucose and non-esterified fatty acids did not.     

Studies on the diurnal rhythm of mevalonate metabolism by sterol and nonsterol pathways and of mevalonate-activating enzymes

Both in vivo and in vitro incorporation of mevalonic acid into nonsaponifiable lipids by 17-day-old chick liver and kidney did not show diurnal rhythm. Using 14CO2 production from MVA as an index of the shunt pathway not leading to sterols, we have demonstrated for the first time that there is no diurnal rhythm in this pathway. No significant differences were found in the specific activities of mevalonate kinase, mevalonate-5-phosphate kinase and mevalonate-5-pyrophosphate decarboxylase from chick liver and kidney throughout a period of 24 hr, using [1-14C]mevalonate as substrate. The absence of diurnal rhythm in the decarboxylase activity was corroborated by further experiments carried out using [2-14C]mevalonate-5-pyrophosphate as specific substrate of this enzyme.     

The regulation of phosphoenolpyruvate carboxykinase (GTP) synthesis in rat kidney cortex. The role of acid-base balance and glucocorticoids.

The effects of metabolic acidosis and of hormones on the activity, synthesis, and degradation of renal cytosolic P-enolpyruvate carboxykinase (GTP) (EC 4.1.1.32) were studied in the rat using isotopic -immunochemical procedures. At normal acid-base balance, the synthesis of the enzyme accounted for between 2 and 3.5% of the synthesis of all soluble protein in the kidney cortex. P-enolpyruvate carboxykinase synthesis was selectively stimulated in acute metabolic acidosis, so that the relative rate of synthesis of the enzyme was increased to 7% 13 hours after oral administration of ammonium chloride. The stimulation of P-enolpyruvate carboxykinase synthesis preceded any increase in the assayable activity of the enzyme. The administration of sodium bicarbonate to acutely acidotic rats returned the rate of enzyme synthesis to normal in 8 hours. The effect of acidosis on both the synthesis and the activity of P-enolpyruvate carboxykinase was prevented by actinomycin D, cordycepin, and cycloheximide. The degradation in vivo of pulse-labeled P-enolpyruvate carboxykinase was not affected by acidosis. Thus, the stimulation of P-enolpyruvate carboxykinase synthesis is the major mechanism for the increase in the level of the enzyme observed in metabolic acidosis. The administration of glucocorticoid triamcinolone resulted in an increase in the relative rate of P-enolpyruvate carboxykinase synthesis and a commensurate increase in the activity of the enzyme in the renal cortex. Both changes were abolished by actinomycin D. Fasting was characterized by a high enzyme activity and a rapid rate of enzyme synthesis in the kidney cortex. This high rate of synthesis was reduced after the administration of sodium bicarbonate, but not after glucose feeding. Moreover, the injection of insulin to diabetic rats did not repress P-enolpyruvate carboxykinase synthesis in the renal cortex. Theophylline plus N-6, 0-2'-dibutyryl adenosine 3':5'-monophosphate stimulated P-enolpyruvate carboxykinase synthesis in the kidney of intact rats. However, the latter effect was probably due to glucocorticoid secretion, since it did not occur in adrenalectomized animals. The administration of parathyroid extracts did not result in the induction of the enzyme. Thus, the hormonal regulation of cytosolic P-enolpyruvate carboxykinase synthesis in the kidney differs markedly from that in the liver.     

Circadian Rhythm of Liver Parameters (Cellular Structures, Mitotic Activity, Glycogen and Lipids in Liver and Serum) During Three Consecutive Cycles in Phenobarbital-Treated Rats

The circadian rhythm of gastric content, serum alkaline phosphatase (alk.P.), serum lipids, body weight (wt), relative (rel.) liver wt, cellular structures (by light- and electron-microscopy), mitotic activity of hepatocytes, glycogen content, protein and lipids in liver was studied in 180 male Sprague-Dawley rats orally treated at 0830-1030 with 50 mg/kg phenobarbital (PB) for 7 days. Thereafter, five PB-treated males and five controls each were studied at 4-hr intervals at 0600, 1000, 1400, 1800, 2200 and 0200 on 3 consecutive days. The lighting schedule in the colony was 12:12 = light/dark (light from 0600 to 1800). Following the rhythm of gastric emptying, the rel. liver wt showed a clear circadian rhythm with a peak at 0800. The rel. liver wt was raised in PB-treated rats at all times of the day. The circadian rhythm of cellular structures was closely related to the hepatic glycogen content which exhibited a clear rhythm with the peak also at 0800, but lowered values were found in PB-treated rats. The mitotic activity of hepatocytes was significantly increased in PB-treated rats but displayed the same circadian rhythm as controls with peaks at noon and troughs at midnight. The well-known hypertrophy of the smooth endoplasmic reticulum in PB-treated rats was not found at 0600, but was fully developed at 1400 and 2200. PB-treatment increased significantly the liver content of cholesterol, triglycerides and phospholipids. Liver cholesterol showed a clear circadian rhythm with peaks at 1800. No rhythm of liver protein, triglycerides and phospholipids was observed. In serum, levels of cholesterol were significantly elevated, those of triglycerides and alk.P. significantly lowered, while those of phospholipids were not affected by the treatment. The three serum lipids, alk.P. and beta-lipoprotein exhibited a clear circadian rhythm, while serum glucose and non-esterified fatty acids did not.     

Diurnal rhythms of pinealocyte ultrastructure, pineal serotonin content and plasma melatonin level in the domestic pig

The study was conducted to investigate diurnal changes in pinealocyte ultrastructure, pineal serotonin content and plasma melatonin concentration in the domestic pig. The immature pigs (n=24) were kept under a cycle of 12 h light : 12 h dark, with a photophase between 0800 and 2000. During the photophase the animals were exposed to direct sunlight. After four weeks the gilts were slaughtered at 0900, 1400, 2100 and 0200. The pineals were removed and divided into two parts - one for quantitative ultrastructural study (by a point count method) and one for serotonin assay. Simultaneously, blood samples were taken for melatonin assay. The relative volume of mitochondria in pinealocyte perikarya was significantly higher at 1400 than at 0200 and 0900 as well as at 2100 than at 0200. The relative volume of Golgi apparatus was higher at 0900 and 1400 than at 0200. The relative volume of dense bodies of the MBB-1 type in pinealocyte perikarya was significantly lower at 1400 and 2100 than at 0900. In contrast, the relative volume of MBB-2 was higher at 1400 than at 0900 and 0200. The numerical density of DCV in perikarya was significantly higher at 0200 than at 1400. No significant differences were found in rough endoplasmic reticulum, lysosomes and multivesicular bodies. The pineal serotonin content showed a prominent rhythm with the maximum at 1400. The plasma melatonin concentration was significantly higher at 0200 than at 0900, 1400 and 2100. The obtained results demonstrate that both pinealocyte ultrastructure and pineal biochemistry in the pig undergo significant changes in the course of the diurnal rhythm.